<!DOCTYPE html>
<html>
  <head>
    <title>滾動的球</title>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" type="text/css" href="../css/HW_4-2.css" >
  </head>
  <body>
    <div class="box">
      <div class="ball">球</div>
    </div>
  </body>
</html>
